I. Field of the Invention
The present invention relates to a sorter for sorting sheets discharged from an image forming apparatus such as a copying machine or a printer and, more particularly, to a sorter having a plurality of vertically stacked sheet storage sections and a moving means rotated upon reception of a rotational force from a driving means, the sorter being operated such that the plurality of sheet storage sections are sequentially moved to a sheet reception position while a distance between the currently operated sheet storage section and the next sheet storage section is increased by rotational movement of the moving means.
II. Description of the Prior Art
In a conventional sorter, vertically stacked sheet storage sections are sequentially moved to a sheet reception position of a sheet discharged from an image forming apparatus and the sheets with copied images are selectively sorted on the sheet storage sections. Conventional sorters of this type are designed to be attached to a corresponding image forming apparatus. For this reason, various techniques have been proposed to make the sorters compact and minimize their installation space so as to reduce the occupation space of a system including an image forming apparatus and a sorter.
Japanese Patent Disclosure (Kokai) No. 59-74856 describes the following technique (to be referred to as a first prior art hereinafter; see FIG. 6 of the first prior art). According to this technique, a plurality of bin trays serving as sheet storage sections are vertically stacked, and a rotary belt-like lift mechanism for moving the (lowermost bin--1) bin trays upward to a sheet reception position and a pawl portion for engaging with and holding the bin trays moved up to the sheet reception position are located on the front side of the bin trays. When the pawl portion is swung by reciprocal movement of a solenoid, the bin trays engaged with and held by the pawl are sequentially moved downward below the sheet reception position so that the sheets are selectively received in the bin trays. After the uppermost bin tray is moved downward, the (lowermost bin--1) bin trays are moved upward again to the sheet reception position.
U.S. Pat. No. 4,328,963 describes the following apparatus (to be referred to as a second prior art; see FIGS. 3 and 4 of the second prior art). In this apparatus, there are provided, at the front end side of the bin trays, disk-like transfer wheels 30 coupled to a motor and having transfer wheel slots to be respectively engaged with pins 17, extending on the side wall surfaces of bin trays 11, and arcuated guide slots 18 for guiding and supporting the bin trays through the pins. By utilizing the elastic force of coiled tension springs 10, the bin trays 11 are moved upward and are engaged with the pins. In this state, the transfer wheels 30 are rotated to guide the pins along the guide slots to increase a distance between each two adjacent bin trays while the bin trays are sequentially moved upward to the sheet reception position.
In the first prior art, a tray moving mechanism can be arranged by a simple mechanism to simplify the overall structure. However, the pawl and the rotary belt-like lift mechanism are arranged at the front surfaces of the bin trays. The overall length of the apparatus is inevitably increased. In addition, since the bin trays are moved while the tray engaged with the pawl is dropped, noise is increased by an impact force upon dropping of the bin tray. In the worst case, the bin trays are damaged.
In the second prior art, the transfer wheels are used to constitute a bin tray transfer mechanism. In addition, these transfer wheels are located on the wall at the side of the front ends of the bin trays. The overall length of the sorter is increased by a radius of curvature of the guide slots because the arcuated guide slots are formed to reciprocate the bin trays along the guide slots so as to facilitate engagement of the transfer wheel slots and the pins extending on the side wall surfaces of the bin trays.
In order to solve the above disadvantages, U.S. Pat. No. 4,466,608 proposes a mechanism having vertical linear guide slots. With this structure, the pins must be vertically and linearly moved along the guide slots although the transfer wheels are subjected to circular movement along the wheel slots. As a result, the pins cannot be smoothly guided.
When the pins are engaged with or disengaged from the wheel slots, the guide direction of the slot is preferably the same as the tangential direction of the corresponding transfer wheel. However, when the vertical linear guide slots are formed, as described above, the diameter of each transfer wheel must be increased to substantially match the tangential direction at the engagement or disengagement position with the vertical line. Alternatively, larger wheel slots must be increased to facilitate the engagement.
However, the former arrangement does not satisfy the request for minimizing the overall length of the sorter. The latter arrangement causes a difficulty in disengagement of the pins from the wheel slots toward the guide slots. As a result, smooth movement of the bin trays cannot be achieved. Either arrangement described above cannot solve the disadvantage of the second prior art.
In the second prior art, since the pins extending on the bin trays must be designed to be engageable with the wheel slots, the bin trays must be kept upward by using the elastic force of the springs, and hence the pins must be urged against the peripheral surfaces of the transfer wheels. However, degradation (fatigue caused by use for a long period of time) of the springs occurs. It is often difficult to urge the pins on the peripheral surfaces of the transfer wheels. As a result, smooth engagement of the bin trays with the wheel slots is disturbed.
Further, since the bin trays are biased by the elastic force of the springs, the line connecting the bin trays and the corresponding springs must be located on the front or side surface side of the sorter, and the resultant structure of the sorter is complicated.
In the second prior art, as shown in FIG. 5 therein, the portion for accommodating a motor for transmitting a rotational force to the transfer wheels greatly extends toward the side walls of the bin trays. As a result, the width of the sorter is increased, and hence the sorter itself becomes bulky.